content: /* Copyright (C) 2016-2018 Alibaba Group Holding Limited
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
      http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  ==============================================================================*/
  
  // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  import com.google.protobuf.Internal.ProtobufList;
  
  import java.util.AbstractList;
  import java.util.Collection;
  import java.util.List;
  import java.util.RandomAccess;
  
  /**
   * An abstract implementation of {@link ProtobufList} which manages mutability semantics. All mutate
   * methods must check if the list is mutable before proceeding. Subclasses must invoke
   * {@link #ensureIsMutable()} manually when overriding those methods.
   * <p>
   * This implementation assumes all subclasses are array based, supporting random access.
   */
  abstract class AbstractProtobufList<E> extends AbstractList<E> implements ProtobufList<E> {
  
    protected static final int DEFAULT_CAPACITY = 10;
  
    /**
     * Whether or not this list is modifiable.
     */
    private boolean isMutable;
  
    /**
     * Constructs a mutable list by default.
     */
    AbstractProtobufList() {
      isMutable = true;
    }
  
    @Override
    public boolean equals(Object o) {
      if (o == this) {
        return true;
      }
      if (!(o instanceof List)) {
        return false;
      }
      // Handle lists that do not support RandomAccess as efficiently as possible by using an iterator
      // based approach in our super class. Otherwise our index based approach will avoid those
      // allocations.
      if (!(o instanceof RandomAccess)) {
        return super.equals(o);
      }
  
      List<?> other = (List<?>) o;
      final int size = size();
      if (size != other.size()) {
        return false;
      }
      for (int i = 0; i < size; i++) {
        if (!get(i).equals(other.get(i))) {
          return false;
        }
      }
      return true;
    }
  
    @Override
    public int hashCode() {
      final int size = size();
      int hashCode = 1;
      for (int i = 0; i < size; i++) {
        hashCode = (31 * hashCode) + get(i).hashCode();
      }
      return hashCode;
    }
  
    @Override
    public boolean add(E e) {
      ensureIsMutable();
      return super.add(e);
    }
  
    @Override
    public void add(int index, E element) {
      ensureIsMutable();
      super.add(index, element);
    }
  
    @Override
    public boolean addAll(Collection<? extends E> c) {
      ensureIsMutable();
      return super.addAll(c);
    }
    
    @Override
    public boolean addAll(int index, Collection<? extends E> c) {
      ensureIsMutable();
      return super.addAll(index, c);
    }
  
    @Override
    public void clear() {
      ensureIsMutable();
      super.clear();
    }
    
    @Override
    public boolean isModifiable() {
      return isMutable;
    }
    
    @Override
    public final void makeImmutable() {
      isMutable = false;
    }
    
    @Override
    public E remove(int index) {
      ensureIsMutable();
      return super.remove(index);
    }
    
    @Override
    public boolean remove(Object o) {
      ensureIsMutable();
      return super.remove(o);
    }
    
    @Override
    public boolean removeAll(Collection<?> c) {
      ensureIsMutable();
      return super.removeAll(c);
    }
    
    @Override
    public boolean retainAll(Collection<?> c) {
      ensureIsMutable();
      return super.retainAll(c);
    }
    
    @Override
    public E set(int index, E element) {
      ensureIsMutable();
      return super.set(index, element);
    }
    
    /**
     * Throws an {@link UnsupportedOperationException} if the list is immutable. Subclasses are
     * responsible for invoking this method on mutate operations.
     */
    protected void ensureIsMutable() {
      if (!isMutable) {
        throw new UnsupportedOperationException();
      }
    }
  }
  